Steering by driving control mechanism



June 29, 1948. w. H. BRUCE ETAL I 2,444,279

STEERING BY DRIVING CONTROL MECHANISM Filed Sept. a, 1945 4 Sheets-Sheet 1 gig/1 I J 1948- w. H. BRUCE ETAL 2,444,279

STEERING BY DRIVING CONTROL MECHANISM Filed Sept. 8, 1945 4 Sheets-Sheet 2 June 29, 1948. w. H. BRUCE ETAL STEERING BY DRIVING CONTROL MECHANISM 4 Sheets-Sheet 3 Filed Sept. 8, 1945 Ill/II,

June 29, 1948. w. H. BRUCE ETAL 2,444,279

STEERING BY DRIVING CONTROL "ECHANISI 4 Sheets-Sheet 4 @m/wzMXo/w 19mm M. Q'wwmZ /glow Q31 fan/3km Filed Sept. 8, 1.945

Patented June 29,1948

STEERING BY DRIVING CONTROL MECHANISM William H. Bruce and Douglas w. Erskine, Springfield, Ill, asalgnors to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a

corporation of Delaware Application September 8, 1945, Serial No. 615,230

5 Claims. (Cl. ISO-9.2)

The invention relates to motor vehicles. and more particularly to motor vehicles of the type which are steered by driving, that is, in which steering is efiected by controlling the drive of ground engaging traction devices at opposite sides of the vehicle.

In such vehicles the necessary provisions for controlling the drivemay be made, according to well-known principles, either with or without the use of a diflerential mechanism between the traction devices. If a differential mechanism is used, the prevalent practice is to control the drive of the traction devices by means of a pair of selectively operable steering brakes, one for each traction device; and if no differential mechanism is used, the drive is usually controlled by a pair of selectively operable steering clutches, preferably of the friction type and usually in combination with a pair of selectively operable supplemental brakes, one clutch and one supplemental brake for each traction device.

The practice of controlling the drive by means of a diii'erential and steering brakes, as well as the practice of controlling the drive by means of steering clutches in combination with supplemental brakes has been widely adopted in tractors, particularly in tractors of the self-laying track type. In both instances the tractor is usually equipped with a pair of hand levers, one for each hand of the operator, and in the first instance, where the tractor is equipped with a differential, the hand levers are arranged to control the steering brakes, whereas in the second instance where the drive is controlled without a differential, the hand levers are arranged to control the steering clutches. It is desirable in order to save the operator from undue fatigue that the mentioned hand levers be operable with a minimum of physical effort, and generally. it is an object of the invention to provide an improved steering control mechanism which will satisfactorily take care of said requirement.

More particularly it is an object of the invention to provide in a motor vehicle of the type in which steering is effected by means of a pair of steering clutches, an improved mechanism (or operating said clutches.

As stated, hereinbefore, the steering clutches are preferably of the friction type, and the necessary power for holding said friction clutches engaged during straight ahead drive is usually supplied by suitable loading springs for the clutches. The mentioned hand levers are connected, respectively, with the steering clutches which function to compress the loading springs and thereby release the clutches upon pull on the hand levers. The clutches, particularly in the glarger size tractors, require a relatively high spring pressure in order to hold them properly engaged, and the leverage afforded by the usual power transmitting linkages is such that the operator must exert considerable manual effort in order to disengage the clutches and hold them disengaged when necessary. Consequently, when the tractor is operated in service which requires frequent manipulation of the steering levers, a good deal of physical work is required on the part of the operator in order to drive the tractor.

In order to relieve the operator from undue physical exertion, booster mechanisms have heretofore been suggested for facilitating operation of the steering clutches, and in certain instances, according to such earlier suggestions, the steering clutches were to be actuated by hydraulic servomotors, and hydraulic power for operating the servomotors was to be derived from the vehicle engine. However, it has been found diiiicult to accomplish the desired end of facilitating operation of the steering clutches in the proposed manner, that is, by means of a pair of hydraulic servomotors and an engine driven .pump mechanism, because proper steering of the vehicle, if it is to be eifected by control of the steering clutches, imposes certain requirements upon the mode of operation of the servomotors. That is, the servomotor for the right hand steering clutch must be operable precisely to move the right hand steering clutch from a fully engaged to a fully disengaged position and to any desired partly disengaged position; to move said clutch from said fully disengaged position and from any partly disengaged position to fully engaged position, and to hold said steering clutch partly or fully disengaged for any desired length of time, all without appreciably affecting the operability and operativeness of the servomotor for the left hand steering clutch; and, on the other hand, the servomotor for the left hand steering clutch must be operable precisely to move the left hand steering clutch from a fully engaged to a fully disengaged position and to any desired partly disengaged position, to move said clutch from said fully disengaged position and from any partly disengaged position to fully engaged position, and to hold the left hand steering clutch partly or fully disengag d for any desired length of time, all without appreciably affecting the operability and operativeness of the servomotor for the right through suitable rpower transmitting linkages hand steering clutch. On the other hand, if the servomotors are to be used for operating steering brakes such as are usually employed in combination with a differential, they must obviously be capable of an analogous mode of operation.

In order to provide for a mode of operation of the servomotors in conformity with the requirements as-outlined hereinabove, and particularly in connection with steering clutches, a. control system has heretofore been suggested which utidisengaging the steering clutchesat times when dependent valve mechanisms, the mentioned previously suggested system requires supplemental valve mechanisms to prevent kick-back" or sudden reengagement of one of the clutches when said clutch has been partly or fully disengaged, and thereafter the other clutch is disengaged by operation of its respective servomotor.

It is an object of the inventionto provide an improved motor vehicle of the type in which steering if effected by driving, and more particularly to provide in such a vehicle an improved steering control mechanism utilizing a pair of hydraulically operable servomotors and a pump mechanism supplied with energy from the vehicle motor for operating the servomotors. In this connection, it is a more specific object of the invention to provide an improved arrangement of a pump mechanism, servomotors and control means forv the latter, in combination with friction devices such as steering clutches or steering lbrakes, for operating such friction devices in conformity with the special requirements as outlined hereinabove, and more particularly to provide a system which will do so without an undue multiplicity of valve mechanisms and fluid passages, and without unduly complicated valve structures.

The conventional manually operated control mechanisms for steering clutches, as heretofore used, have ordinarily been so constructed that the amount of pullwhich must be exerted upon the hand levers in order to disengage the clutches increases, due to the increasing resistance of the loading springs, as the hand levers are moved towards their fully disengaged positions, and with such control mechanisms operators often acquire a habit of moving the hand levers only far enough to partially disengage the clutches at times when it would be appropriate to move the hand levers to positions corresponding to full disengagement of the clutches. Obviously, such a habit of operating the steering clutches is very objectionable because of the resulting rapid wear of the friction material. Moreover, the heat which is generated when power is transmitted through the partially engaged clutches for an undue length of time may result in a breakdown of the friction material, and it may also cause failure of the clutches due to overheating of the loading springs and consequent loss of spring tension.

A further object of the invention is to provide in a motor vehicle of the type in which steering is effected by means of a pair of steering clutches, an improved steering control mechanism by means of which operation of the steering clutches is sufficiently facilitated so that an operator may drive the vehicle, without undue fatigue, in continuous service under conditions requiring frequent operation of the steering clutches, and so that the operator will no longer be liable to fall into the aforementioned-habit of only partially they should be fully disengaged.

A further object of the invention is to provide an improved hydraulically operable control mechanism, as set forth hereinbefore, in which a pair of manually operable control levers, one for each steering clutch, are arranged so that the levers tend to adjust themselves automatically to clutch engaged positions, and in which the steering clutches may be gradually disengaged in response to progressive movement of their respective control levers in clutch releasing directions, and vice versa; and in which each clutch may be maintained, if desired or necessary for proper steering, in any condition of partial disengagement by adjusting its respective control lever to and holding it in a corresponding position inter mediate the fully engaged and the fully disengaged positions of the clutch;

A further object of the invention is to provide in a control system of the above character a servomotor and pump arrangement which may be installed on and removed from the vehicle as a compact unit while the steering clutches are in place on the vehicle, and to provide such a unit which may be manufactured at relatively low cos s.

The foregoing and other objects and advantages of the invention will become more fully apparent from the following description of a preferred embodiment of the invention shown in the accompanying drawings. Referring to the drawings, in which like reference characters designate the same or similar parts in the several views:

Fig. 1 is a sectional side view of a crawler tractor, showing the location and general arrangement of the improved control mechanism for the steering clutches on the rearward body part of the tractor;

Fig. 2 is a partial rear view of the tractor shown in Fig. 1, the view being taken partly in section on line 1-1 of Figs. 1 and 4 to show the steering clutches and associated control mechanism;

Fig. 3 is a view, on line III-III of Fig. 2, showing a shift yoke for the steering clutch at the left side of the tractor, and its connection (in section) with the hydraulically operable control mechanism;

Fig. 4 is a top view of part of the hydraulically operable control mechanism for the steering clutches, a large housing enclosing certain parts of the mechanism being shown in full view, and a top aperture of the housing, which is normally closed by a cover, being shown exposed to afford a view of inside parts of the housing;

Fig. 5 is a side view of the hydraulically opera'ble control mechanism for the steering clutches, the right hand part of this view being a section on line V-V of Fig. 4, and the left hand part of Fig. 5 showing a pair of manually operable control levers and their mounting on the tractor body;

Fig. 6 is an end view of Fig. 5 showing the mounting of the manually operable control levers on the tractor body;

Fig. 7 is a section on line VII-VII of Fig. 4, showing cylinder bores and fluid passages in the upper part of the mechanism;

Fig. 8 is a section on line VIII-VIII of Fig. 4;

Fig. 9 is an enlarged view similar to Fig. 4 but showing parts of the mechanism in section on of the mechanism practice, comprises a main frame and a pair of endless track mechanisms at opposite sides, respectively, of the main frame; a power plant and suitable mechanism for transmitting power from the power plant to the endless track mechanism being mounted on the main frame. The power plant as shown in Fig. 1 comprises an internal combustion engine I and accessories therefor such as a radiator 2, an air cleaner 3 and a fuel tank 4, the radiator and air cleaner being mounted in proximity to the engine on a forward part of the main frame, and the fuel tank in the present instance being mounted on a rearward part of the tractor. A throttle control lever for the engine is indicated at 6, and an operator's seat I is mounted on the main frame in front of the fuel tank 4.

The mechanism for transmitting power from the engine i to the endless track mechanisms at opposite sides of the tractor, comprises a master clutch of conventional construction not shown and which is enclosed in a bell housing 8 at the rear of the engine, a propeller shaft 5, a change speed transmission enclosed in a housing Ii and comprising an output shaft I2, a counter shaft i3 and a gear shift lever I4; and means for steering the tractor by driving enclosed in a rear housing structure i5 of the main frame and controlled by a pair of hand levers l8, and 18' (Figs. 1 and 6). V

The endless track mechanisms at opposite sides of the main frame are of identical and conventional construction, each comprising a track frame [8 which is pivoted on the main frame for vertical swinging movement abouta transverse axis indicated at i9. Endless track belts 2| and M (Fig. 2) are mounted for travel around the track frames by means of track rollers and front idlers (not shown) and by means of track belt the propeller shaft I. then through any selected gear combination of the change speed transmission and through intermeshing bevel gears 84 and 38 to a cross shaft 31 which carries drivingdrums 38 and 38', respectively. of the steering clutches; and then simultaneously through stacks of clutch disks and through driven drums GI and II of the steering clutches to nnai drive plnions l3 and 43' which are permanently geared to thevtrack belt drive sprockets 23 and 23', respectively. :lirough suitable gearing as indicated at 48 and The cross shaft ll which carries the bevel gear 18 extends through aligned openings in partitions ll and 4! of the rear housing II. and the cross shaft 31 is mounted in said openings by a pair of conical roller bearings ii and II. The driving drums "and II of the steering clutches are bolted, respectively, to radial flanges of drivdrive sprockets, the latter being indicated at 23 a and 23 in Fig. 2. The track belt drive sprockets are mounted on the main frame for rotation about the mentioned pivot axis i 9, and a transverse leaf spring 26 supports the main frame on forward portions of the track frames, all in conformity with generally accepted practice. A drawbar for hitching a load to the tractor is indicated at 21.

Referring to Fig. 2, it will be noted that for purposes of illustrating the invention, a tractor has been selected in which the drive of the traction devices is controlled without the use of a difierential, a pair of steering clutches being indicated generally at 28 and 28', and a pair of supplemental brakes being indicated at ii and 3 I The brakes are controlled in conformity with conventional practice by foot pedals, respectively, one of which is shown at .33 in Fig. 1. For straight ahead driving both of the steering clutches are fully engaged and the supplemental brakes are released so that both track belt drive sprockets 23 and 23' may be rotated in unison by the driving torque of the engine I. Such driving torque is transmitted from the crank shaft of the engine through the master clutch at 8 to ing' hubs l3 and it. which are non-rotatably mounted on the cross shaft 31 at opposite ends of the latter. A circumferential series of axially extending outer keys are formed on the drum 30. and the latter is surrounded by a stack of clutch disks comprising a number of metallic internally toothed disks 8 which are drivingly engaged bythe keys of the driving drum It, and by a number of externally toothed friction disks 81 which are drivingly engaged at their outer peripheries by internal axially extending keys of the driven drum l1 and alternate with the metallic driving disks 8'. A flange 55 is interposed between the driving hub 53 and the driving drum 3| to aiford an axial abutment for the stacked clutch disks I, 81. The driven drum II is mounted on a large flange ll of the supporting shaft for the final drive pinion l3, and the brake band 3! surrounds the drum 4i and may be tightened thereon for braking purposes through a suitable mechanism, not shown, which is operable by the foot pedal 33.

Axial pressure for compressing the stack of disks i6 and 51 is supplied by a circumferential series of coiled loading springs 58 which are ar-- ranged at the inside of the driving drum 8! and are seated axially on radial lugs projecting towards the interior of the drum 3' at the end of the latter remote from the driving hub 53. The free ends of the coil springs 58 adjacent to the driving hub 53 bear against an axially floating ring 59 which carries a plurality of long bolts 6| corresponding in number to the number of loading springs 58, the bolts ii extending axially, respectively, through the coiled springs 58. Mounted on the bolts II is a thrust plate 62 for exerting pressure upon the stacked clutch disks It, 51 towards the driving hub 53. The loading springs 58 are under appreciable initial tension and they subject the ring I! to a strong axial pressure in the direction towards the driving hub 53. Such axial pressure upon the ring I! is transmitted to the thrust plate 62 through the bolts 8 i the heads of the latter bearing against the thrust plate at the side of the latter remote from the driving hub 53. Tubular spacers 6! surrounding the bolts Ii are interposed between the floating ring I! and the thrust plate 62 for securing the latter at a predetermined axial distance from the ring 59.

The driving hub 51 has a central sleeve portion for mounting a spider N thereon, the spider being fitted upon the sleeve portion for shifting movement axially thereof and having abutment arms extending axially through suitable apertures of the driving hub towards the floating ring 5!. A

shifter yoke 88 for moving the spider 88 axially back and forth on the sleeve'portion of the driving hub 58 is mounted on the hub of the spider by means of a ball bearing 81.

The left hand steering clutch 28' is a duplicate of the right hand steering clutch 28, as will be apparent from an inspection of Fig. 2. Clutch disks 58' and 51' corresponding to the clutch disks 58 and 51 are operativcly interposed between the driving drum 38' and the driven drum 4i, and in conformity with the corresponding parts of the right hand steering clutch the left hand steering clutch comprises an abutment flange 55', initially tensioned loading springs 58', an axially floating ring 59', bolts 8|, a thrust plate82', tubular spacers 68' and a spider 64'. A clutch shifter yoke 88' for the left hand steering clutch 28' is mounted on the hub of spider Gl'by means of a ball bearing 61'.

Referring to Fig. 3, the outer race of the ball bearing 81' carries a pair of diametrically opposed Journal bearings for the reception of journals 88 and 89 which are rigidly mounted on the shifter yoke 88', and the latter is thus swingable about a horizontal axis at right angles to the shaft 31. At a lower portion of the yoke 88 a thrust button 'I I is mounted on the latter opposite to a complementary thrust button 12' on the retainer for the roller bearing 52.

Swinging movement of the yoke 66' about the axis of the Journals 88, 69 in a direction to force the thrust button ll against the thrust button 12' causes axial shifting movement of the spider 84' towards the driving hub 53. Such shifting movement of the spider is transmitted through the arms of the latter to the axially floating ring 58', and the resulting axial shifting movement of the ring 59' is transmitted to the thrust plate 82' through the tubular spacers 83'. The axial distance between the thrust plate 82' and the abutment flange 55' will therefore be increased when the yoke 86' is moved in the mentioned direction which is indicated by the arrow A in Fig. 2. However. such movement of the yoke 66' is strongly resisted by the pressure of the loading springs 58' which, like the loading springs 58. are under appreciable initial tension. and which tend to move the yoke 88' in a direction opposite to that indicated by the arrow A until the entire pressure of the loading springs is taken up by the abutment flange 55' through the stacked clutch disks 58', 51'. The stacked clutch disks 56', 51' are thus normally subject to axial compression by the initial tension of the loading springs 58', and when .the stack of clutch disks is thus compressed frictional engagement of disks 56 with the disks 51' establishes a drivin connection between the driving drum 38' and the driven drum Ii. The length of the tubular spacers 63' is such that when the thrust plate 82' is fully drawn up against said spacers by the bolts 8|, as shown in Fig. 2, the loading springs 58' are sufficiently compressed to exert the necessary axial pressure to which the stacked clutch plates must be subjected in order to prevent slippage between the clutch disks under the maximum torque which is to be transmitted from the driving drum 38' to the driven drum 8!. From these explanations it will be aparent that the steering clutch 28 is fully engaged when the parts are positioned as shown in Fig. 2, and that the clutch 28'. may be gradually released by swinging movement of the yoke 88' from the position in which it is shown in said figure about the axis of the journals 68, 89 in the direction indicated by the arrow A in Fig. 2.

The foregoing explanations with respect to the construction and operability of the left hand steering clutch 28' similarly apply to the construction and operability of the right hand steering clutch 28. The latter clutch. like the left hand steering clutch, is fully engaged as shown in Fig. 2, and it may be gradually released by swinging movement of the shift yoke 88 inthe direction of arrow A. The thrust buttons II and 12 at the lower end of the shift yoke 88 correspond to the. thrust buttons II and 12' of the shift yoke 88'.

The hand levers l8 and i8 which, as mentioned hereinbefore, are mounted on the tractor in front of the driver's seat I serve to control the steering clutches 28 and 28'. respectively. More specifically, the hand levers serve to control a pair of hydraulic servomotors which in turn are operatively connected with actuating members for the steering clutches, that is, with the shifter yokes 88, 88'.

' Referring to Figs. 2, 4 and 5, the central compartment of the rear housing l5 of the main frame, which encloses the bevel gears 88 (Fig. 1) and 28 (Fig. 2) has an oblong top opening I8, and the lateral compartments of the housing l5 which contain the steering clutches 28, 28', and the brakes 8|. II, have relatively large top openings l4 and I8, respectively, which are normally closed byremovable covers, not shown. Mounted on top 'of the housing 15. between the clutch compartment openings 18, 14' and over the central top opening I8, is a one-piece support 11 in the form of a casting which, as shown in Fig. 4, comprises a forward cylinder block and a rearward housing portion. The support 11 is secured to the top wall of the housing is by four short bolts 18 which extend through lateral flange portions I8 of the cylinder block, and by three short bolts 88 which extend through a flange 8| at the rear of the housing portion of the support ll. Referring to Fig. "l which shows a vertical transverse section through the forward cylinder block, the latter comprises two horizontal barrel portions 82 and "which extend side by side in the longitudinal direction of the tractor and which are connected with each other by a web 88. Vertical webs 88 connect the barrels 82 and 88. respectively, with the flange portions 18, and the space between the webs 88 and below the barrels 82, 88 and below the web 88 is open at the bottom and communicates with the interior of the housing i5 through the mentioned central aperture 13 of the latter. However, the mentioned space below the barrels is closed at its forward end by a vertical transverse wall portion which merges with the barrels 82 and 83 and extends between the flange portions 18, and said transverse wall portion has a lower flat surface 81 as indicated in Fig. 5 for seating the cylinder block on the top of housing IS. The forward part of the top opening 18 is thus closed bythe forward part of the support TI, and a long bolt 88 extends through a solid part of the support 11 between the barrels 82, 88, as shown in Fig. 5, to further secure the support 11 to the housing l5.

The barrel portions 82 and 88 merge at their rearward ends with the mentioned housing portion of the support I1, and as shown in Figs. 4 and 5 said housing portion comprises a vertically disposed continuous circumferential wall 88, a central raised bottom wall portion 8| merging at its front and rear ends with the circumferential wall 88. andlateral bottom wall portions" and 88 (see Fig. 8) which are disposed on a common level with the flange portions 19 and 8|. The lateral bottom wall portions merge at their front and rear ends, and at their sides remote from the central raised portion 9|, with the circumferential wall 89. and they also merge with the central raised portion 9I along the longitudinal edges of the latter. The verticalcircumferential wall 89 has a continuous inturned flange 94 along its upper edge, and four bolt holes 98 extend through the vertical wall 89 and through the flange 94 at one side of the support 11, which side is the right side on the tractor, for the reception long bolts 91 (Fig. by means of which the support 11 is further secured to the top wall of the housing I5. A corresponding series of bolt holes 98' are provided for the same purpose at the other side of the support 11, which other side is the left side on the tractor. A cover 98 for the housing portion of the support 11 is retained on the flange 94 by the bolts 91, as shown in Fig. 5, but for the purpose of exposing the interior of the housing portion the cover 98 is omitted in Fig. 4. Additional bolt holes 99 are provided in the flange 94 and in the circumferential wall 89 for the reception of short bolts I9I (Fig. 5) by means of which the cover 98 is additionally secured to the support 11. As shown in Fig. 5, the cover 98 has a filler opening which is normally closed by plug I92, and said filler opening is fitted with a strainer I93. It will be seen that the central top opening 13 of the housing I5 is entirely covered by the one-piece support 11, and a gasket, not shown, is preferably interposed between the housing I5 and the support 11, such gasket surrounding the top opening 13.

A one-piece sump I04 is secured to the support 11 below the latter and extends through the top opening 18 of the housing I5 into the bevel gear compartment of the latter between the partitions 48 and 49, as shown in Figs. 2 and 5. The sump I94 has a bottom wall I 90, a rear wall I01, vertical longitudinal side walls merging with the bottom wall I06 and with the rear wall I91, and a forward manifold head I08 extending between and merging with the longitudinal side walls. The sump I94 is secured to the underside of the central raised bottom portion 9| of the support 11 by bolts I99 which extend through the raised bottom portion 9I of the support, one of the bolts I09 being screwed into a tapped hole in the rear wall I91 of the sump, and the other two bolts I09 being screwed into tapped holes in the right and left side walls, respectively. of the sump. The raised bottom portion 9i of the support 11 has a substantially V-shaned boss III overlying the manifold head I98 of the sump, as shown in Figs. 2. 4 and 5, and three bolts II2 extend through the boss III into tapped holes of the manifold head I08 to addit onally secure the sump I94 to the support 11. The portion of the sump between the rear wall I91, the manifold head I08, and the right and left side walls of the sump is open at the top, and the housing portion of the support. 11 communicates with the sump through two relativel large bores I I3 in the central raised bottom portion 9| of the support 11. A gasket, not shown, is preferably interposed between the bottom portion 9| of the support 11 and the top of the sump I04, and as shown in Fig. 2, the sump I94 has a recessed portion at its lower left hand corner to afiord clearance for port 11 and diverge forwardly from the V-shaped boss III, the portionsof the ribs which extend between the boss III and the vertical circumferential wall 88 of the support rising from the raised bottom portion 8| of the support 11, as shown in Fig. 8, and the portions of the ribs which extend between the circumferential wall 88 and the front end of the cylinder block projecting downwardly from the barrel portions 82 and 83, respectively, as shown in Fig. 7. A straight horizontal fluid passage II1 extends through the rib II4 from a vertical flat front face of the barrel portion 82 into the boss III, and a short vertical bore III which is drilled into the boss III from the underside of the support 11 merges with the rear end of the horizontal passage II1, as best shown in Figs. 2 and 4. Another. straight horizontal fluid passage II9 extends through the rib 6 from a vertical flat front face of the barrel portion 83 into the boss III, and a short vertical bore I2I which, like the bore H8, is drilled into the boss III from the underside of the support 11, merges within the boss III with the rear end of the passage II9, as shown in Figs. 2 and 4.

The short vertical bores I I8 and I 2I of the boss III communicate at their lower ends with internal passages I22 and I23, respectively, of the manifold head I98 of the sump I94. As shown in Fig. 2, the passage I 22 extends obliquely downwardly and to the right of the manifold head and then continues horizontally in a forward direction towards the forward end of the sump I94, as shown in Fig. 5. The internal passage I23 of the manifold head I08 likewise extends obliquely downwardly to the right and then continues horizontally in a forward direction, below the horizontal portion of the passage I22, towards the forward end of the sump, as shown in Figs. 2 and 5. The front face of the manifold head I98 extends in a vertical plane and contains two holes formed by the passages I22 and I23, respectively, one above the other and both oil'set towards the right, as indicated in Fig. 2. In addition to the holes formed by the passages I22, I 23, the front face of the manifold head contains a relatively large central aperture in communication with a cavity I24 of the sump which is indicated in Fig. 5. The cavity I 24 is bounded by the bottom and side walls of the sump,,by the manifold head I08, and by a skirt portion I28 of the manifold head I 08, and a. hole I21 is formed in the lower part of the skirt portion I28 through which hole the cavity I24 communicates with the part of the sump in rear of the manifold head I08, this latter part of the sump communicating. as stated, with the housing part of the support through holes H8. The passages I22 and I23 communicate with a pump mechanism I28 which is mounted on'the sump I94 at the forward end of the latter and which is shown in Figs. 8. l9 and 11. 0

Referring to Figs. 10 and 11, the pump mechaanism I28 is a twin pump unit of the gear wheel positive displacement type and, in effect, constitutes a compact assembly of two individual gear pumps which are operable in unison to draw fluid,

preferably 011, from the sump I94 and to deliver such fluid under pressure into the manifold passages I22 and I28, one of th gear pumps supplying the passage I22 and the other supplying the passage I23. As shown in Figs. 19 and 11, the twin pump unit comprises a polygonal central body portion I29 which is axially recessed from both ends to provide a forward gear chamber I3I, a rearward gear chamber I32 and a central vertical partition I88 between the gear chambers.

The partition I33 has an axial aperture I34, as ShOWII n 11, through which the gear chambers communicate with each other. and a pair of rotary shafts I36 and I31 are journaled in axial bores of the partition in laterally offset relation to the aperture I34. A front cover I38 and rear plate I39 provide additional supports for the shafts I36 and I31. A pair of intermeshing pump gears I 4I and I42 are integrally formed, respectively, with the shafts I38 and I31, and are enclosed in the forward gear chamber I3I. Another pair of intermeshing pump gears I43 and I44 are mounted, respectively, on the shafts I36 and I31 and are enclosed in the rearward gear chamber I32, the gear I43 being non-rotatably secured to the shaft I36 by a key I48. The body part I29, the cover I38 and the rear plate I39 are tightly held together by ten long bolts I41 which extend through aligned holes of these parts and are threaded into tapped holes of the sump casting I84, the'rear face of the plate I39 bearing tightly against the vertical front face of the sump I84.

2 I 42, and a horizontal bore I59 is drilled into the body I29 from the rear face of the latter. and terminates in the pocket I58. The end plate I39 has an axial through-bore I6I, as shown in Fig. 8. in communication with the horizontal bore I59 of the pump body I29, and the through-bore I8I, therefore, constitutes the discharge port of the forward pump unit. The bore or discharge port I6I communicateswith the manifold passage I22 which in turn communicates with the horizontal oblique fluid passage II1 (Fig. 4) of the support 11, as explained hereinbefore andas indicated by dash-dotted lines in Fig. 8. It will thus be seen that when the pump shaft I38 is rotated in the direction of arrow C in Fig. 11, the forward pair of pump gears I4I, I42 and the rearward pair of pump gears I43, I44 will simultaneously draw oil fromthe sump I84, and the forward pair of pump gears I4I, I42 will discharge oil under pressure through the discharge port I8I, manifold passage I22 and vertical bore II8 into the oblique horizontal fluid passage II 1 of the support 11,

1 while the rearward pair of pump gears I43, I44

The shaft I36 extends forwardly through the I cover I38, and a spur Sear I48 is keyed to the forwardly projecting end of the shaft I36. As shown in Figs. 1 and 5, the transmission counter shaft I3 extends rearwardly from the transmission casing I I into the rear housing I5. and a gear I49 in constant mesh with the gear I48 is mounted on the splined rearend of the transmission countershaft I3 for supplying the pump mechanism I28 with energy from the tractor motor I. The countershaft I 3 of the transmission is permanently geared through a pair of gears I5I, I52 to the propeller shaft 9, in conformity with conventional practice, and therefore the pump mechanism I28 will be driven whenever the engine I is running and the master clutch at 8 is engaged, irrespective of whether the change speed transmission controlled by the gear shift lever I4 is in gear. or in neutral.

Referring again to Fig. 11, the arrow 0 indicates the direction of rotation of the pump gears MI and I43 when the engine I is running and the master clutch is engaged, as mentioned hereinabove. The end plate I39 has a fluid inlet passage I53 (Fig. 8) in axial alignment with and of the same configuration as the passage I34 shown in Fig. 11, and said inlet passage I63 of the endplate I39 communicates with the aforementioned cavity I 24 of the sump. The sump I84 and the housing portion of the support 11 are normally filled with oil approximately to the level indicated by the dash-dotted line I54 in Fig. 5, and when the gears HI and I43 rotate in the direction of arrow C, 011 will therefore be drawn from the sump I04 into the pump mechanism. The end plate I39, as shown in Fig. 8, further has an axial through bore I58 which communicates with a pocket I51 of the rearward gear chamber I32 at the pressure side of the pump gears I43 and I44. Accordingly, when the shaft I36 is driven, as mentioned hereinbefore, the rearward pump gears I43, I44 will continuously deliver pressure fluid through the bore I58, which constitutes the discharge port of the rearward pump. unit, into the manifold passage I23 which in turn communicates with the horizontal oblique fluid passage II9 (Fig. 4) of the support 11 as explained hereinbefore, and as indicated by dash-dotted lines in Fig. 8.

The forward gear chamber I3I of the pump body I29 has a pocket I58, similar to the pocket I51, at the pressure side of the pump gears I,

will simultaneously discharge oil under pressure through the discharge port I58, manifold passage I23 and vertical bore I2I into the oblique horizontal passage II9 of the support 11.

The forward portion of the support 11 which has been referred to hereinabove as a cylinder block and which comprises the two barrel portions 82 and 83', has two cylinder bores I62, I63, the bore I62 extending'clear all the way through the barrel portion 82, and the bore I63 extending clear all the way through the barrelportion 83. Secured to the cylinder block at the forward end of the latter are two plunger brackets I84, I65, the plunger bracket I64 having an annular shoulder I64 fitted into the,cylinder bore I62 as shown in Fig. 9, and the plunger bracket I65 having an annular shoulder I65 fitted into the cylinder bore I83. The plunger bracket I64 is suitably flanged for bolting to a flange portion I86 of the barrel portion 82, the flange portion I86 having five blind tapped holes I68, as shown in Fig. 'I, for the reception of mounting bolts I61 shown in Fig. 4, and the plunger bracket I65 is similarly secured to a flange portion I86 of the barrel portion 83 by five mounting bolts I69 screwed into blind tapped holes I68.

Reciprocably mounted in an axial bore of the bracket I64 is a solid plunger I1 I, the bore for the plunger ill in the bracket I 64 comprising three sections on an axis coinciding with the axis of the cylinder bore I62, namely, a first relatively short section I12 adjacent the forward end of the bracket I84, which is of substantially larger diameter than the plunger IN, a second still shorter section I13 which is of smaller diameter than the section I12 but of larger diameter than the plunger HI, and a third section I14 of substantial length which extends between the section I13 and the rear face of the annular shoulder I 64', and whichis of a suitable diameter to afford a close but sliding fit of the plunger I1I in the bracket I64. The body portion of the plunger I1I has a smooth cylindrical outer surface of substantial length so that the plunger may be moved axially a considerable distance into the cylinder bore I62, and so that it may be moved forwardly to a position in which its rear end projects a relatively short distance rearwardly from the annular shoulder I64. At its forward end the plunger I1I carries a coupling head I16 which has a hole I11 (Fi 9) for the reception of a coupling pin I18 as shown in Fig.

5. A seal I19 (Fig. 9) surrounding the plunger III is mounted in the forward bore section I12 of the plunger bracket I to close the gap between the plunger Ill and the circumferential surface of the bore section- I12. The bore section I'll provides an annular space behind the seal I'll for a purpose which will be explained here-' inbelow. I

Referring to Figs. and 6, a mounting bracket IlI for the hand levers I6 and I6 issecured by bolts I92 to the forward end of the transmission housing II. The bracket III comprises two transversely spaced vertical arms I92 and I, and a cross pin I96 is supported at its opposite ends in the arms I" and I. The hand levers I6 and I6 are pivoted at their lower ends on the cross pin I66 and extend upwardly therefrom between the arms Ill and I. The upper end of the bracket arm I9: is forked. and the lever I6 has a stop lug I61 between the prongs of the forked arm I63, the stop lug Ill being engageable with one or the other of the prongs of the arm I to limit back and forth movement of the lever I6 about the pin I. The hand lever II has a stop lug I61 similar to the stop lug Ill, which is engageable with one or the other of two prongs formed at the upper end of the arm I94, for limiting back and forth movement of the hand lever I6 about the cross pin I96.

In Fig. 5 the hand lever I6 is shown in full lines in its rearmost position which corresponds to full disengagement of the right hand steering clutch 26, and the hand lever I6 is shown in dashdotted lines in its foremost position which corresponds to full engagement of the left-hand steering clutch 26'. The hand lever I6 is operatively connected with the plunger III bymeans of a turnbuckle I99 which has a forward forked end embracing the hand lever I6 and a rearward forked end embracing the head I16 of the plunger III, a pin I9I pivotally securing the forward forked end of the turnbuckle to the hand lever I6, and the mentioned pin Ill pivotally securing the rearward forked end of the turnbuckle to the plunger head I16. A bellows I92 of flexible material, such as oil-proof rubber, is secured at its forward end to the plunger I'll and at itsrear end to a collar of the plunger bracket I64 to provide a protective enclosure for the body portion of the plunger III and the seal I19.

The plunger bracket I66 is an opposite hand duplicate of the plunger bracket IN, and the explanations given hereinabove with respect to the plunger bracket I'll similarly apply to the plunger bracket I66. That is, the plunger bracket I69 has a bore on an axis coinciding with the axis the cylinder bore I63 and comprising three sections I12, Ill and I'll. A seal I19 corresponding to the seal I19 is mounted in the bore section "2. Reciprocably mounted in the bore section I14 of the bracket I66 is a solid plunger III which is an exact duplicate of the plunger I'll and which is operatively connected with the hand lever I6 in the same manner as explained hereinbefore in connection with the plunger I'll and the hand lever II. a turnbuckle I99, corresponding to the turnbuckle I", being indicated in Figs. 1 and 6 and pivotally secured to the hand lever I6 by apin I9I'.

As shown in Figs. 5 and 9, the plunger bracket.

I64 has a vertically extending cavity I99 at its rear end below the bore section I", the cavity 14 municates with the cylinder bore I62, and the cavity I99 thus forms an open fluid inlet passage at the forward end of the cylinder bore I62. Similarly, the plunger bracket I66 has a cavity I99 at its rear end, corresponding to the cavity I92 of the plunger bracket I64, the cavity I99 communicating at its lower end with the oblique horizontal fluid passage H9, and the upper part of the cavity I93" communicates, below the bore section I14, with the cylinder bore I69. The cavity I92 thus forms an open fluid inlet passage at the forward end of the cylinder bore A piston I96 is reciprocably mounted in the cylinder bore I62, as best shown in Fig. 9, the piston I96 having a relatively long cylindrical outer surface of a diameter slightly smaller than the diameter of the cylinder bore I62 so as to provide a close but sliding fit of the piston within the cylinder. For this purpose the cylinder bore may be honed and the piston ground so that the diameter of the latter will be slightly smaller.

say ten thousandths of an inch, than the diameter of the cylinder bore I62. The piston I96 comprises a body portion and a skirt portion extending rearwardly from'the body portion, a forwardly tapering socket I99 being formed in the rear part of the body portion and having a spherical seat at its forward end. A set of four rearwardly diverging fluid passages I99 are drilled into the body portion of the piston I96, these passages being equally distributed circumferentially of the piston, as indicated in Fig. 8. The passages I99 are open at their rear ends and communicate at their forward ends with a central recess 29I in the forward part of the piston, the recess having a circular chamfered edge 292 providing a conical valve seat. The plunger III has a short conical portion 299 at its rearward end of the same bevel as the chamfer 292, and as will be further referred to hereinbelow, the conical portion 299 of the plunger "I may be moved into engagement with the valve seat 292 so as to close the recess "I and, therefore, the fluid passages I99. I

A piston I96 which is an exact duplicate of the piston I96 is reciprocably mounted in the cylinder bore I63, and the piston I96 is closely but slidably fitted into the cylinder bore I69 in the same manner as has been explained hereinbefore in connection with the piston I96 and the cylinder bore I62. The same reference characters which have been used in the description of the piston I96 are applied, in Fig. 9, to the piston I96 but are prime-indexed to denote their correlation with the piston I96, and the description of piston I96 similarly applies to the piston I96. The plunger III has a short conical portion 299' at its rearward end which may be moved into engagement with the valve seat 292 of the piston I96 so as to close the recess 2" and, therefore, the fluid passages I99 of the piston I96.

Referring again to Figs. 4 and 8, a pair of vertically disposed rock shafts 294 and 294' are mounted on the support I'l within the housing portion of the latter, a boss 291 for mounting the rock shaft 294, and a boss 296 for mounting the rock shaft 294'. being formed within the housing portion of the support 11 at the left and right sides, respectively, of the latter. As shown in Fig. 2, the portion of the support TI on which the boss 291 is formed overlies the lateral compartment of the housing l6 which encloses the right hand steering clutchltand the portion of the support 'I'I on which the has 200 is formed overlies the lateral compartment of the housing I! which encloses the left hand steering clutch 20'.

Fitted into the boss 20'! is a bearing sleeve 200 which extends downwardly into the compartment for the steering clutch 20 through a hole in the top wall of the housing I0, and the sleeve 200 is secured against axial displacement within the boss 20'! by a set screw H0. The rock shaft 2001s journaled in the bearing sleeve 200 and has an upper end projecting into the housing part of the support 11, and a lower end projecting into the compartment for the right hand steering clutch 28. The portion of the rock shaft 20, below the bearing sleeve 200, is splined and has a circumferential groove, and the portion of the rock shaft 204 above the bearing sleeve 208 is similarly splined and grooved, as shown'in Fig. 8. A lower rock arm 2 for connecting the rock shaft 200 with the shift yoke of the right hand steering clutch 20 is detachably mounted on the lower end of the rock shaft 200, a hub of the rock arm 2 having internal splinesmatching the lower splines of the rock shaft to secure the rock arm against rotary displacement on the rock shaft. The hub of the rock arm 2 also has a radial vertical split and a bore at right angles to the split for the reception of a clamping bolt 2I2 which is partly received in the lower circumferential groove of the rock shaft, to secure the rock arm against displacement axially of the rock shaft. By tightening the bolt M2 the rock arm 2 may be securely fastened on the rock shaft 204, and upon removal of the bolt M2 the rock shaft 204 and the rock arm 2" may be readily separated from each other in the axial direction of the shaft 204. The bolt M2 is accessible through the top opening 14 (Fig. 2) of the housing is.

Another rock shaft 204' which is an exact duplicate of the rock shaft 200, is rotatably mounted in the boss 200 of the support II by means of a bearing sleeve 209' corresponding to the bearing sleeve 209, the bearing sleeve 200' being retained in the boss 200 by a set screw 2I0'. Detachably secured to the lower end of the rock shaft 204' is a lower rock arm 2" which is an exact dupli-- cate of the rock arm 2H, a clamping bolt 2I2' corresponding to the clamping bolt 2I2 being accessible through the top opening ll (Fig. 2) of the housing It.

Fig. 3 shows the connection between the lower rock arm 2" and the shift yoke 08' of the left hand steering clutch 20'. The shift yoke 80 of the right hand steering clutch 20 and the lower rock arm 2 of the rock shaft 204 are connected with each other in the same manner as shown in Fig. 3. Referring to Fig. 3, the free end of the rock arm 2] I' has a vertical bore lined with a bushing 2" which embraces a ball head 2 I0 on the shift yoke 66, and rocking movement of the shaft 204' about its axis within the bearing sleeve 200' is transmitted through the lower rock arm 2" and ball head 2 to the shift yoke 00' so that the latter will swing sidewise about the axis of the journals 80, 60 in response to said rocking movement of the rock shaft 200'. Similarly, the shift yoke 06 for the right hand steering clutch is swingable sidewise in response to rocking movement of the rock shaft 204 about its axis within the bearing sleeve 200.

The upper end of the rock shaft 204 has longitudinal splines and a circumferential groove, as stated, the same as the lower end, and an upper rock arm 2 I0 is detachably secured on the splined hub of the upper rock arm is indicatedat 2 I8 and the clamping bolt at 2I9. Pivotally connected with the free end of the upper rock arm 2I6 by means of a pivot pin 22l is a thrust rod 222, the pin 22I extending through a forked rearward end of the rod 222 which embraces an eye at the free end of the arm M6. The thrust rod 222 has a spherical forward end for abutment against the piston I98, the forward end of the thrust rod 222 being seated in the socket I98 of the piston I00 and its spherical forward end being adapted to bear against the spherical forward end of said socket I98.

The thrust rod 222, the upper rock arm 2I8. the rock shaft 204 and the lower rock arm 2 operatively connect the piston I96 with the shift yoke 88 of the right hand steering clutch 28, and-the shift yoke 66' of the left hand steering clutch 28 is operatively connected with the piston I96 by a thrust r 222', an upper rock arm 2l6', rock shaft 200' and lower rock arm 2| I, and the partsforming said last named connection are duplicates of the correspondingly designated parts of the connection between the piston I98 and the shift yoke 66 of the right hand steering clutch. A pivot pin 22I' connects the rear end of the thrust rod 222' with the upper rock arm 2I6', and the latter is secured in position on the rock shaft 204 by a clamping bolt 2 I 9'.

The operation of the hereinabove described control mechanism for the steering clutches is as follows: Figs. 1 and 5 show the hand lever IS in its foremost position, and as stated hereinbefore and as will appear hereinbelow, said position of the hand lever I6 corresponds to full engagement of the left hand steering clutch. Similarly, the foremost position of the hand lever it corresponds to full engagement of the right hand steering clutch, and with both levers I 8, l6 adjusted to their foremost positions both track belts may be driven simultaneously to propel the tractor on a straight course.

Fig. 9 shows the plunger I'll partly projecting into the cylinder bore I62, and the turnbuckle I89 (Fig. 5) is adjusted to such a length that when the hand lever I6 is in its foremost position the conical rear'end 203 of the piston ill will be spaced a relatively short distance from the rear face of the annular shoulder I, as shown in Fig. 9. The left hand plunger I'll is shown in Fig. 9 as being rearwardly displaced relative to the plunger ill, the conical rear end 203' of the plunger IIl being spaced a relatively great distance from the rear face of the annular shoulder I 85'. The right hand plunger III may be moved rearwardly by rearward swinging movement of the hand lever I6, and when the latter hand lever is in its rearmost position, the distance of the conical rear end 203 of the plunger ill from the rear face of the annular shoulder I64 will be the same as the distance at which the conical rear end 203' of the plunger III is spaced in Fig. 9

-' from the rear face of the annular shoulder I65.

. l7 tance as that at which the conical rear end 266 of the plunger Ill is shown in Fig. 9 from the rear face of the annular shoulder I64, the tumbuckle I 69' (Fig. 1) being properly adjusted to position the conical rear end 266' of the plunger III at the mentioned distance from the rear face of the shoulder I66 when the hand lever I6 is in its foremost position, as shown in Fig. l.

The lower and upper rock arms 2i I and 2 I6 are secured to the rock shaft 264 in a predetermined angular relation to each other, as indicated by the angle a in Fig. 9, and'the lower and upper rock arms 2i I and 2I6' are secured to the rock shaft 264' in the same predetermined angular relation to each other, as indicated by the angle a. The piston I66 is shown in Fig. 9 as being spaced at sufllcient distance from the conical rear end of the plunger ill to keep the recess 26I open, and the forward spherical end of the push rod 222 is shown as engaging the forward spherical end of the socket I 66. The angular displacement of the rock arms 2 and 2I6 as indicated by the angle a is such that the piston I96 may occupy the position in which it is shown in Fig. 9 while the shift yoke 66 (Fig. 2) of the right hand steering clutch 26 is in the position in which it is shown in Fig. 2, and which position, as stated, corresponds to full engagement of theclutch 26. The full pressure of the initially tensioned loading springs 56 is effective to hold the right hand steering clutch engaged while the shift yoke 66 is positioned,.as shown in Fig. 2, and while the piston I96 and the plunger. III are positioned as shown in Fig. 9. The heavy pressure exerted by the loading springs "upon the floating ring 69 while the clutch 26 is engaged affords a strong resistance against swinging movement of the shift yoke 66 in the direction of arrow A in Fig. 2, and, consequently, rearward movement of the piston I96 from the position in which it is shown in Fig. 9 is likewise strongly resisted by the initial tension of the loading springs 66.

The foregoing explanations with respect to the relative angular displacement of the rock arms 2 and III on the rock shaft 264 similarly apply to the angular displacement of the rock arms II I and 2" on the rock shaft 264', these latter rock arms being mounted on the rock shaft 264' in the same angular relation to each other as the rock arms 2 and 2I6 are mounted on the rock shaft 264, the angle a in Fig. 9 between the rock arms 2| I' and 2I6' being the same as the angle a between the rock arms 2 and 2I6. According- 1y, when the hand lever I 6' is adjusted to its foremost position as shown in Fig. 1 the piston I96 in the cylinder bore I66 may be spaced from the rear end of the plunger III to keep the piston recess 26I' and the passages I99 open while the left hand steering clutch is fully engaged. The loading springs 66' of the left hand steering clutch 26' strongly resist rearward movement of the piston I66 in the cylinder bore I63, because of the heavy pressure which the loading springs 66' exert upon the floating ring 59' when the left hand steering clutch is engaged.

In connection with the description of the pump mechanism I26 (Fig. it has been explained hereinbefore that when the tractor motor I is running and the master clutch at 6 is engaged, the forward pump comprising the gears MI and I42 continuously discharges pressure fluid into the manifold passage I22, and that the rearward pump comprising the gears I46, I44 continuously discharges pressure fluid into the manifold passage I26. The manifold passage I22 communicates through the vertical bore II6, the oblique horizontal passage Ill and the cavity I96 with the cylinder bore I62, and when the plunger III and the piston I96 are positioned as shown in Fig. 9, the pressure fluid entering the cylinder I62 will be discharged from the space in front of the piston I96 to the space in rear of said piston through the open recess 2IlI and the fluid passages I99. The cylinder space in rear of the piston I 96 communicates with the interior of the housing part of the support I1, and the pressure fluid discharged from the open passages I99 will therefore pass into the housing portion which, as stated, communicates with the sump I64 through the two large bores 6. In other words, when the lever I6 is in its foremost or clutch engaged position, the forward pump I4I, I42 will merely be effective to circulate oil from the sump I64 through the cylinder space in front of piston I96 back to the sump I64, and the piston I96 will be subject to no appreciable hydrostatic pressure which would tend to move the piston I 96 rearwardly and disengage the right hand steering clutch 26. Only a slight hydrostatic pressure will be efiective in front of the piston I96 to keep the plunger Ill and the piston I69 separated from each other.

In order to disengage the right hand steerin clutch 26 th operator pulls rearwardly on the handle end of the lever I6 and thus initiates rearward movement of the plunger I'II from the position in which said plunger is shown in Fig. 9. As a result of such rearward movement of the plunger I'II its conical rear end 296 will come to bear on the conical valve seat 262, and the outlet passages I99 will be closed, with the result that the pressure fluid entering the cylinder space in front of the piston I 96 can no longer escape to the cylinder space in rear of the piston I96. Hydrostatic pressure will therefore quickly build up in front of the piston I96 and become high enough to start the piston I96 rearwardly against the pressure of the loading springs 66. A relatively light steady rearward pull On the handle end of the lever I6 will be sufllcient to keep the conical rear end 266 of the plunger ill in sealing contact with the valve seat 262 while the piston I96 moves rearwardly under the pressure of the fluid entering the cylinder bore I62 and accumulating in front of the piston I96, The steering clutch 26 may thus be fully disengaged without appreciable manual eflort, the pump I4I, I42 actually doing the work of moving the piston I 96 rearwardly against the heavy and steadily increasing resistance of the loading springs 56. When the hand lever I6 arrives in its rearmost position which is determined by engagement of the stop lug I6'I (Fig. 6) with the rear prong of the bracket arm I66. as shown in Fig. 5, the piston I96 recedes a short distance from the conical rear end of the plunger I I I and as a result, an amount of pressure fluid equal to the amount of pressure fluid entering through the inlet port I93 will escape through the outlet passages I99 while the lever I6 is kept in its rearmost position and while the piston I96 is subject to a relatively high hydrostatic pressure which will maintain the clutch 26 disengaged. The operator may thus keep. the

right hand steering clutch fully disengaged. for any desired length of time by maintaining a relatively light rearward pull on the handle end of lever I6 while the latter is in its rearmost position.

From the foregoing explanations with respect to the control of the right hand steering clutch by means of the hand lever I6, the control of the left hand steering clutch by means of the hand lever I6 will be apparent. The lefthand cylinder bore I63 is continuously supplied with pressure fluid by the rearward pump I43. I44 through passages I23, I2I, H9 and cavity I93, and Fig. 9 shows the positions which the plunger HI and the piston I96 occupy when the left hand steering clutch is maintained fully disengaged by bydrostatic pressure upon the piston I96. It will be noted that the gap between the conical rear end 203 of the plunger HI and the valve seat 202 as shown in Fig. 9 is very small, a relatively small gap being suflicient to permit escape of an amount of pressure fluid equal to the amount entering through the inlet port I93 while the left hand steering clutch is kept fully disengaged by hydrostatic pressure in front of the piston I96.,

Fig. 4 shows the upper rock arm 2I6 in the same position as that in which it is shown in Fig. 9, and to which it may be moved in the above described manner by rearward movement of the hand lever I6 to its rearmost position.

When the hand levers I6, I6 are in their foremost or clutch-engaged positions and the pumps I4I, I42 and I43, I44 are driven by the tractor engine the pressure fluid discharged from the pump I 4|, I42 circulates, as stated, through the space within the cylinder I62 in front of the piston I96, and the pressure fluid discharged from the pump I43, I44 circulates through the space within the cylinderl63 in front of the piston I 96, The fluid pressure within'the mentioned cylinder spaces is relatively low, under these conditions, but when the discharge passages I99, I99 are closed by rearward movement of the plungers I1I, I1I' the fluid pressure in the mentioned cylinder spaces rises to a relatively great height. The plungers III, I1I are closely but slidably fitted into the bore sections I14, I14 of the plunger brackets I64 and I65, respectively, and when the accumulated fluid in front of the pistons I96 and I96 is under relatively high pressure, any seepage through the bore sections I14,

I14 past the plungers I1I, I1I' will reach the bore sections I 13, I13. In order to dispose of the fluid seeping into the bore sections I13, I13, said bore Sections, are connected with the housing part of the support 11 through bleeding passages as best shown in Fig. 9. Drilled into a longitudinal rib at the outer side of the barrel portion 82. as indicated in Fig. 7, is a, straight horizontal bore 221, and a similar bore 221' is drilled into a longitudinal rib at the outer side of the barrel portion 83. The plunger bracket I64 has an angular passage 228 which connects the bore section I13 with the forward end of the bore 221. and the plunger bracket I65 has a similar angular passage 228' which connects the bore section I13 with the forward end of the bore 221'. The bores 221 and 221' communicate at their rear ends with the interior of the housing part of the support 11, and fluid seeping past the plungers I1I, I1I' through the bore sections I14, I14 will be returned from the bore sections I 13, I13, through angular passages 228, 228' and horizontal passages 221, 221 to the housing part of the support 11 and from the latter to the sump I04 through the bores I I3.

In operation of the tractor it is sometimes desirable, and under certain conditions necessary, that for the purpose of making a turn the corresponding steering clutch be not fully disengaged. For instance, if a heavily loaded trailer is hitched to the drawbar 21 and the vehicle train 20 proceeds downhill on a grade, full disengagement of one of the steering clutches would create a serious hazard because the vehicle train may jack-knife and turn over under the push or the trailer. For the purpose of avoiding such an accident the steering clutches must be operable reliably and precisely to control the drive of the track belts, that is, the steering clutches must be gradually disengageable to any desired extent and they must be capable of being precisely held in any condition of partial disengagement for any desired length of time. The clutch control mechanism herein disclosed is particularly suitable to satisfy this important requirement. Rearward movement of the hand lever I6 from its foremost position. as explained hereinbefore, brings the conical rear end of the plunger I1I into sealing engagement with the valve seat 202, and the outlet passages remain closed as long as the operator follows up the rearward movement of the piston I96 by rearward movement of the hand lever. It will be seen, however, that the piston I 96 may be arrested at any point of its travel within the cylinder bore I62, it being only necessary for the operator to discontinuethe mentioned rearward follow-up movement of the hand lever I6. 1 When the operator stops said followup movement of the hand lever I6 at any point short of the rearmost or fully disengaged position of the hand lever, the piston I96 will recede a very short distance from the arrested plunger III, and the same amount of pressure fluid which enters through the inlet port I93 into the cylinder space I62 in front of the piston I96 will then be discharged through the outlet passages I99, and fluid under pressure in front of piston I96 will be effective to prevent forward movement of the piston under the more or less heavy counterpressure of the loading springs 58, the

extent of said counterpressure depending on the extent of disengagement of the clutch. Thus, the operator is able to disengage the right hand steering clutch either fully or partly to any desired extent and to keep the clutch fully or partly disengaged for any desired length of time. The position of the hand lever I6 is an accurate indication of the degree of clutch disengagement, and the clutch respondsquickly and accurately to movement of the hand lever I6. From any intermediate position of the hand lever I6 the latter may be moved either forwardly to gradually reengage the clutch, or rearwardly to gradually disengage the clutch more fully.

The foregoing explanations with respect to partial disengagement of the right hand steering clutch similarly apply to the left hand steering clutch, and it will be seen that the left hand steering clutch 28' will quickly and accurately respond to back and forth movement of the hand lever I6, the same as has been described hereinabove in connection with the hand lever I6 and right hand steering clutch 28.

The control system described in detail heresystem more clearly. To avoid crossing of the fluid passages, the pump gears I43, I44 are shown in Fig. 12 in front of the pump gears I4I,- I42.

and the other of the servomotors comprising the cylinder I93 and the piston Ill and being supplied with pressure fluid by the pump I43, I44. The bore I59 (Fig. 8) in the end plate I39 of the pump unit forms an open discharge passage of the pump I43, I44, and said open dischargepassage communicates with the open inlet passage I93 (Fig. 4) of the servomotor I93, I93 through the passages II9, I2I and I23 (Figs. 2 and 4). Similarly, the bore I 59 (Fig. 11) in the pump body I29 and the bore IiI (Fig. 8) in the end plate I39 of the pump unit form an open discharge passage of the pump I4I, I42, and said open discharge passage I59, I9I communicates with the open inlet passage I93 (Fig. 4) or the servomotor I82, I99 through the passages H1, H9, I22 (Figs. 2 and 4). In other words. the passages II9, I2I and- I23 constitute flui'd conduit means having open ends at I53 and I83 in communication, respectively, with the pressure side of the pump I43, I44, and with the cylinder bore I53 at a point remote from the open end of the latter; and the passages III, I I8 and I22 constitute fluid conduit means having open ends at iii and I93 in communication, respectively, with the pressure side of the pump I4I. I42, and with the cylinder bore I92 at a point remote from the open end of the latter. The reciprocable parts of the servomotors, which in the illustrated embodiment of the invention are the pistons, have fluid outlet passages I99, I 99. respectively, the recesses 2M, 2M aflording fluid outlet ports at the Pressure sides of the pistons I98, I99, respectively. The plungers Ill, III' constitute manually adjustable followers for closing the outlet ports 2III, 2III', respectively. The reciprocable parts of the servomotors are operatively connected, respectively, with actuating members of friction devices, for moving said actuating members upon delivery of pressure fluid through the inlet passages I93, I93 and upon closure of the outlet ports 2, 2M. The friction devices, in the illustrated embodiment of the invention are represented by the clutches 29, 29', but it will be obvious that the system lends itself to use in connection with other types of friction devices for controlling the drive of traction devices at opposite sides of a motor vehicle.

Referring to Figs. 1 and 5, it will be noted that the support 11 and enclosed parts, together with the sump I04, the pump mechanism I 29, and the plunger brackets I 94, I" may readily be installed, as an assembled unit, on and removed as an assembled unit from the tractor while the steering clutch 28, 29' and the shift yokes 36. 69' are in place on the tractor. The bolts 2I2, 2I2' for securing the lower rock arms 2| I, 2| I to the rock shafts 294, 204 are accessible, as stated, through the top openings I4, I4, respectively, of the housing II, and the lower rock arms 2H, 2" may therefore be disconnected from the rock shafts 294, 204 preparatory to removal of the mentioned assembled unit from the tractor. Likewise, the mounting bolts 39, 33, 91 and the pivot pins I'll for the turnbuckles I99, I99 may be removed preparatory to removal of the mentioned assembled unit from the tractor. In order to install the assembled control mechanism on the tractor, an analogous procedure may be followed, as will be readily understood from the foregoing explanations.

It should be understood that the invention claimed herein is not limited to the exact details of design and construction disclosed, and it is 22 contemplated as including modifications within the scope of the appended claims.

It is claimed and desired to secure by Letters Patent: I

1., In a motor vehicle of the type having ground engaging traction devicesat opposite sides thereof and means for steering said vehicle by drivin comprising a pair of friction devices and separate actuating members therefor selectively operable, respectively, to control the transmission of power to said traction devices, the combination of a pair of hydraulic servomotors each comprising a stationary part having an open fluid inlet passage, a reciprocable part having a fluid outlet passage, and control means operable to open and close said outlet passage; means operatively connecting said reciprocable parts, respectively, with said actuating members for mov ing the latter upon delivery of pressure fluid through said inlet passages and closure or said outlet passages, and a pair of fluid pumps supplied with energy from the vehicle motor and having open discharge passages in communication, respectively, with said fluid inlet passages for individually supplying said servomotors with pressure fluid.

2. In a motor vehicle of the type having ground engaging traction devices at opposite sides thereof and means for steering said vehicle by driving comprising a pair of friction devices and actuating members therefor operable, respectively, to control the transmission of power to said traction devices, the combination of a pair of hydraulic servomotors each comprising a stationary part mounted on the vehicle body and having an open fluid inlet passage, a reciprocable part having a fluid outlet passage, and a control member fitted into said stationary part for reciprocating movement relative thereto in the same direction as said reciprocable part and being abuttable with the latter to close said fluid outlet passage; means operativeiy connecting said reciprocable parts, respectively, with said actuating members for moving the latter upon delivery of pressure fluid through said inlet passages and closure of said outlet passages; and a pair of fluid pumps drivingly connected with the vehicle motor and having open discharge passages in communication. respectively, with said fluid inlet passages for individually supplying said servomotors with pressure fluid.

3. In a motor vehicle of the type having ground engaging traction devices at opposite sides thereof and means for steering said vehicle by driving comprising a pair of friction devices and actuating members therefor operable respectively, to control the transmission of power to said traction devices, the combination of a pair of cylinders mounted on the vehicle body and each having an open fluid inlet port adjacent to one end thereof; a pair of pistons mounted, respectively, within said cylinders and each having a pressure side facing said one end of its respective cylinder, and a fluid discharge port at said pressure side; manually adjustable followers for said pistons mounted, respectively, n said cylinders and movable against said pressure sides of said pistons to close said discharge ports; thrust transmitting means operable. respectively, by said pistons upon advance movement thereof from said one end of their respective cylinders towards the other. to move said actuating members, and a pair of fluid pumps drivingly connected with the vehicle motor and having open discharge passages in communication, respectively, with said fluid inlet ports for individually supplying said cylinders with pressure fluid.

4. In a motor vehicle. of the type hav n ground engaging traction devices at opposite sides thereof and means for steering said vehicle by driving-comprising a pair of friction devices and actuating members therefor operable, respectively, to control the transmission of power to said traction devices, the combination of a pair of cylinders mounted on the vehicle body and each having an open fluid inlet port adjacent to one end thereof, a pair of pistons mounted; respectively, within said cylinders and each having a pressure side facing said one end of its respective cylinder, and a fluid discharge port at said pressure side; manually adjustable followers for said pistons mounted, respectively, on said cylinders, each of said followers comprising a cylindrical stem portion of smaller diameter than its respective piston reciprocably and sealingly fitted into an axial aperture of its respective cylinder at said one-end thereof, and a seat on said stem portion engageable with the discharge port of the respective piston for closing said discharge port; thrust transmitting means operable, respectively, by said pistons upon advance movement thereof from said one end of their respective cylinders towards the other, to move said actuating members, and a pair of fluid pumps drivingiy connected with the vehicle motor and having open discharge passages in communication respectively, with said fluid inlet ports for individually supplying said cylinders with pressure fluid.

5. In a motor vehicle of the type having ground engaging traction devices at opposite sides thereof and means for steering said vehicle by driving comprising a pair of friction devices and separate actuating members therefor selectively operable, respectively, to control the transmission of power to said traction devices.

the combination of fluid storage means. a p ir of cylinders having open ends, respectively, in

communication with said fluid storage means, a

pair of fluid pumps communicating at their suc- 5 tion sides with said fluid storage means and operable tocontinuously draw fluid from said storage means,lflul d conduit means having open ends in communication, respectively, with the pressure side of one of said pumps and with one of said cylinders at a point remote from said open end of the latter, other fluid conduit means independent of said first mentioned fluid conduit means having open ends in communication, respectively, with the pressure side of the other of said pumps and with the other of said cylinders at a point remote from said open end of said other cylinder, a pair of pistons reciprocably mounted, respectively, in said cylinders and having passages to permit continuous circulation of fluid by said pumps through said conduit means and piston passages, a pair of individually adjustable followers for said pistons cooperable, respectively, with said pistons to close said piston passages, and means operatively connecting said pistons, respectively, with said actuating members of said friction devices for moving said actuating members by movement of said pistons in response to accumulation of pressure fluid in said cylinders upon closure of said piston passages. 30 WILLIAM H. BRUCE. DOUGLAS W. ERSKINE.

REFERENCES CITED The following references are of record in the 35 file of this patent:

UNITED STATES PATENTS Number Name a Date 1,921,590 Staude Aug. 8, 1933 0 2,337,637 Brown Dec. 28, 1943 2,379,628 Eberhard et al July 3, i945 

